An economizer consists of a flash tank or heat exchanger with an associated dedicated expansion device and piping. It is located in a refrigeration circuit downstream of the condenser. In the case of the heat exchanger, as is specifically disclosed, the flow upstream of the economizer circuit is divided with a minor portion of the condensed refrigerant flow passing through an expansion device thereby undergoing a pressure drop and partially flashing as it passes into the economizer heat exchanger. In the economizer heat exchanger, the remaining liquid refrigerant evaporates due to heat transfer with the major portion of the condensed refrigerant which is further cooled, thereby increasing the cooling capacity of the unit. The gaseous minor flow is at an intermediate pressure and can pass to the compressor, to cool the motor, or it may be supplied directly to intermediate compression volumes in the compressor to increase the mass of refrigerant being compressed.
Because the economizer flow line leading to the compressor is connected to a variable pressure inside the intermediate compression volumes, the flow may go back and forth as the intermediate compression volume pressure changes. The present invention places a variable restriction in the economizer line supplying the intermediate compression volumes which may be trapped volumes, as in a positive displacement compressor, or interstage for a multiple stage compressor. The size of the restriction affects the efficiency and capacity of the economized cycle. However, the optimum restriction size varies with operating conditions. For example, for higher pressure ratio applications the optimal size of the restriction or injection port is larger than for lower pressure ratio applications. The present invention varies the size of the restriction as a function of compressor operating conditions to maximize the unit operating efficiency or capacity. Additionally, there is also an optimum size of the restriction or injection port for maximum unit capacity and the opening would be larger if the unit is optimized for maximum capacity rather than for maximum efficiency operation.
In some refrigeration systems, such as transport refrigeration, the temperature is very precisely controlled and may be held to 0.1xc2x0 C. Accordingly, in such systems, the suction and discharge temperatures and/or pressures are monitored in addition to the zone temperatures etc. and provide the necessary information for controlling the size of the restriction or injection port.
It is an object of this invention to provide a method and apparatus to increase the efficiency and/or capacity of a refrigeration system cycle.
It is another object of this invention to precisely control the economizer flow into a compressor to variably control refrigeration system capacity. These objects, and others as will become apparent hereinafter, are accomplished by the present invention.
Basically, the economizer flow to the intermediate compression volumes is controlled via a variable restriction or injection port which is optimized to maximize efficiency and/or capacity and/or to vary capacity.